I'd have said, Neither. Having worked briefly on cleaning crews, I believe that the work comes in larger and more predictable blocks than waiting tables does, and leaves one more time for thinking one's own thoughts.

No, you can't tell about a person's skillset. I teach ESL, and have taught

  a. An employee of the the Brazilian national health department now cleaning houses in Montgomery County, Maryland.
  b. A Nicaraguan attorney now cleaning rooms for a Washington, DC, hotel.
  c. A Salvadoran archivist doing construction work here.

And forty years ago, I caught a cab driven by a man from west Africa with a degree in urban planning, who had found it better for his health to leave his native country, where he was not well regarded by the government.

And there are plenty of native-born Americans who are holding down jobs that are not commensurate with their skills or anyway potentials.